function z = ps(x)
%Powell singular function
%n=4,m=4,x0=[3,-1,0,1]
%fmin1=f13([0;0;0;0])=0 
%Author:Ji Lin
z(1)=x(1)+10*x(2);
z(2)=5^(1/2)*(x(3)-x(4));
z(3)=(x(2)-2*x(3))^2;
z(4)=10^(1/2)*(x(1)-x(4))^2;
z=sum(z.^2);
